1. Field of the Invention
The present invention relates to nozzles and, more particularly, to a nozzle including a circular exhaust orifice having a periphery composed of an edge formed by the intersection of two concentric surfaces of revolution.
2. Description of the Prior
The use of ultrasonic waves to nondestructively inspect composite laminate parts for porosity, delaminations, defects in bonding, and the presence of foreign objects, is well known. Testing with ultrasonic waves requires that a coupling medium, typically water, be used to conduct the ultrasonic waves between the transducer and the test object. Early apparatus required submersion of the test object, while more recent devices use a nozzle to produce a column of water that extends between the transducer and the test object and contains the ultrasonic waves.
Current ultrasonic testing devices are of two types, pulse echo and through transmission. Pulse echo devices measure the difference in time between the transmitted waves and the waves respectively reflected by the test piece, while through transmission apparatus measure the attenuation of the transmitted waves after they pass through the test piece. The former apparatus require one column of water between the emitting transducer and the test piece, while the latter additionally require a second column of water to couple the test piece with a receiving transducer.
When the flow in the column of water becomes nonlaminar, the column breaks up and the internal reflection of the ultrasonic waves contained in the column becomes scattered rather than remaining focused. Nonlaminar flow also causes an increase in the number of droplets reflecting off the test part and impinging onto the column to cause turbulence. For the foregoing reasons, the signal to noise ratio of the ultrasonic waves being transmitted in the column of water decreases as the flow becomes nonlaminar.
The distance between the nozzle and the test piece is known as the throw distance. Ultrasonic testing devices using the nozzles of the prior art avoid the onset of an unacceptable signal to noise ratio by keeping the throw distance less than that which would lead to nonlaminar flow and, concomitantly, an unacceptable signal to noise ratio. With the nozzles of the prior art, the maximum throw distance when the column of water is horizontal is typically two to three inches.
In a number of newer structures, protrusions such as flanges, fibs, co-cured stiffeners and other structural supports oftentimes prevent using the nozzle within this limited throw distance. The ever increasing presence of these protrusions coupled with the inherent limitations of the prior art nozzles restricts the beneficial use of the automated ultrasonic scanning devices that have been developed.
The transition to nonlaminar flow in the water column exhausted by a nozzle is also a function of flow rate, with the throw distance at which nonlaminar flow occurs decreasing as the flow rate increases. The flow rate must be low enough to prevent nonlaminar flow from occurring within the throw distance over which the nozzle is intended to provide an acceptable signal to noise ratio. However, the prior art nozzles typically require a flow rate that is so low that the column of water droops due to gravity when the column is horizontal.
Among other problems, droop causes a difference between the location actually being inspected and the inspection location on the test piece calculated by the computer program used by the automated ultrasonic scanning device. This error occurs because the software cannot accurately compensate for droop, especially when the contour of the surface of the test piece rapidly changes.